With industrial development, the concentration of carbon dioxide in the atmosphere has been increasing due to the consumption of large amounts of fossil fuels, thus increasing global warming. Changes in climate caused by global warming have been responsible for the imbalance of the ecosystem in which the amount of carbon dioxide in the atmosphere is not maintained at a constant level through the carbon cycle, and such changes will be accelerated in future. Hansen and Lebedeff reported an increase in the average temperature of the earth, and general circulation models (GCMs) predict that the surface temperature of the earth will increase. Accordingly, since the international convention on climate change, including a protocol for greenhouse gas reduction, was established, studies on the development of various technologies capable of efficiently removing carbon dioxide are being conducted.
All land plants perform the process of photosynthesis by which the plants synthesize carbohydrates from water and carbon dioxide using solar light as an energy source. In European advanced countries, carbon dioxide is being efficiently recovered by increasing forests using photosynthesis, and forest products are being used in various applications. However, there are a lot of obstacles in removing carbon dioxide using land plants. This is because land plants very slow photosynthetic rates leading to low carbon dioxide fixation rates.
According to reported studies, the use of microalgae (phytoplanktons living in water) allows the fixation rate of carbon dioxide per unit area to be increased by several times to several tens of times. Thus, studies focused on fixing carbon dioxide into starch are being actively conducted.
However, in order to practically use a process of fixing carbon dioxide directly from industrial exhaust gases using a microalgal culture process, the following several problems should first be solved. It is known that industrial exhaust gases have a carbon dioxide content of about 10% for LNG combustion gas or bituminous gas, although the carbon dioxide content varies depending on the type of fuel used. Thus, in order to use microalgae to remove carbon dioxide, the microalgae must be capable of surviving in the above-described range of carbon dioxide content and need to have high carbon dioxide fixation rate. Also, because the exhaust gases contain components inhibiting the growth activity of the microalgae, for example, sulfur oxide (SOx) and nitric oxide (NOx), the microalgae need to have excellent resistance to these components, and also needs to be rich in biomass so that it is industrially used in practice.
Accordingly, it is urgently required to develop microalgae, which have excellent resistance even to high concentrations of carbon dioxide, sulfur oxide (SOx), nitric acid (NOx) and the like and also have a high carbon dioxide fixation rate and are rich in biomass.